1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device which exhibits a high vibration damping or isolating effect based on flows or resonance of the fluid contained therein. More particularly, the invention is concerned with such a fluid-filled damping device simple in construction and which is capable of exhibiting an excellent vibration damping effect utilizing fluid flows.
2. Discussion of the Related Art
As a vibration damping device, there is known a fluid-filled elastic mount or vibration damper interposed between two members in a vibration system in order to connect these two members or support one of the two members by the other member in a vibration damping manner. Examples of such a fluid-filled vibration damping device are disclosed in JP-A-57-9340, JP-A-61-62633, JP-U-61-191543, JP-A-61-270533, JP-A-4-296237, and JP-A-8-4826. The vibration damping devices disclosed in these publications have a plurality of fluid chambers which are filled with a non-compressible fluid such as water, and an orifice passage. The fluid is forced to flow between the chambers of the original passage, so as to exhibit a vibration damping or isolating effect based on the resonance of the fluid through the orifice passage. In these fluid-filled vibration damping devices, the orifice passage is tuned to a specific frequency range of the vibration to be damped, by suitably determining the cross sectional area of fluid flow and the length of the orifice passage. Thus, these vibration damping devices exhibit an excellent vibration damping effect based on the flows of the fluid through the orifice passage.
In recent years, various attempts have been made to provide a fluid-filled vibration damping device which even further improves vibration damping capability. However, none of these attempts have been successful in providing such a fluid-filled vibration damping device, which also has a simplified structure which is economical to manufacture.
To improve the damping effect based on the flows of the fluid through the orifice passage, it is effective to increase the length of the orifice passage. However, an increase of the length of the orifice passage inevitably requires an increase of the cross sectional area through fluid flow of the orifice passage (i.e., so that the orifice passage remains tuned to the desired frequency range of the vibration to be damped). However, it is not practical to increase the length and cross sectional area of fluid flow through the orifice passage in order to improve the vibration damping effect of the device, since the provision of such an orifice passage requires a large space within the device.
Another method of improving the vibration damping effect of the vibration damping device, attempts to increase an amount of the fluid flow through the orifice passage by positively controlling the pressures of the fluid in the fluid chambers. However, in order to control the fluid pressures, the vibration damping device needs to be equipped with an actuator and a control device for controlling the actuator. This undesirably increases the complexity of the structure of the device and the cost of manufacture.